A PENCIL BEAM MODEL FOR PHOTON DOSE CALCULATION
A PENCIL BEAM MODEL FOR PHOTON DOSE CALCULATION
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DOI：
10.1118/1.596856
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发表时间：
1992-03-01
期刊：
影响因子：
3.8
通讯作者：
TREPP, A
中科院分区：
文献类型：
--
作者：
AHNESJO, A;SAXNER, M;TREPP, A
提出了一种利用铅笔束能量沉积核计算放射治疗计划中的光子剂量的方法。它的设计是为了满足三维治疗规划算法的要求，该算法足够通用，可以处理入射到异质患者身上的不规则形状的辐射场。它是面向点的，因此比全三维卷积算法更快，并使用与全三维卷积算法相同的物理数据库来表征临床束流。结果表明，结合蒙特卡罗能量沉积核和在水模中测量的剂量分布，可以非常准确地表征光子治疗光束。这些数据被用来得出解析的铅笔束核，这些核被大致划分为来自(I)初级释放的电子和正电子，(Ii)散射的、韧致辐射的和湮没的光子，(Iii)污染的光子和(Iv)来自准直器头部的带电粒子的剂量。提出了一种基于场三角剖分的半解析积分方法，利用解析核进行剂量计算。剂量以归一化到入射能量通量的单位计算，这便于输出系数的计算。对于在非均匀介质中的应用，使用沿射线路径的单向卷积来导出散射校正因子。在均匀介质中，用蒙特卡罗计算和Batho方法将结果与测量结果和在非均匀介质中进行了比较。
A method for photon dose calculation in radio therapy planning using pencil beam energy deposition kernels is presented. It is designed to meet the requirements of an algorithm for 3-D treatment planning that is general enough to handle irregularly shaped radiation fields incident on a heterogeneous patient. It is point oriented and thus faster than a full 3-D convolution algorithm and uses the same physical data base to characterize a clinical beam as a full 3-D convolution algorithm. It is shown that photon therapy beams can be characterized with great accuracy from a combination of precalculated Monte Carlo energy deposition kernels and dose distributions measured in a water phantom. The data are used to derive analytical pencil beam kernels that are approximately partitionated into the dose from (i) primary released electrons and positrons, (ii) scattered, bremsstrahlung, and annihilation photons, (iii) contaminating photons, and (iv) charged particles from the collimator head. A semianalytical integration method, based on triangulation of the field, is developed for dose calculation using the analytical kernels. Dose is calculated in units normalized to the incident energy fluence which facilitates output factor calculation. For application in heterogeneous media, a scatter correction factor is derived using monodirectional convolution along the ray path. In homogeneous media results are compared with measurements and in heterogeneous media with Monte Carlo calculations and the Batho method.